1. Field of the Invention
The present invention relates in general to a head drum apparatus of a VCR(Video Tape Cassette Recorder), and particularly to an apparatus with an improved assembly accuracy by making a head-affixing surface, a rotor transformer-affixing surface and a bearing-engaging surface be at the same height and to an apparatus with an improved engaging accuracy when a rotating shaft and an upper drum are engaged.
2. Description of the Conventional Art
Conventionally, a head drum apparatus, as shown in FIG. 1, includes a lower drum 5 rigidly affixed to a supporting plate 50. A rotating shaft 1 rotatably passing through the center portion of the lower drum 5 is engaged with upper and lower bearings 3 and 4. An upper drum 2 is rotatably engaged to the upper portion of the rotating shaft 1. A rotor 11 of a motor assembly 6 is rigidly engaged to the lower portion of the rotating shaft 1, that is, below the lower drum 5. Here, the motor assembly 6 includes a stator 13 affixed to the lower portion of the lower drum 5 and a rotor 11 rotatably affixed to the lower portion of the rotating shaft. In addition, a ring collar 12 rigidly affixed to the rotor 11 is rigidly affixed to the rotating shaft 1. The lower surface of the upper drum 2 and the upper surface of the lower drum 5 are facing each other. A plurality of head assemblies 7 between the lower surface of the upper drum 2 and the upper surface of the lower drum 5 are rigidly affixed to a predetermined portion of the lower surface of the upper drum 2. A rotor transformer 9 disposed at the inside portion of the head assembly 7 is rigidly affixed to a predetermined portion of the lower surface of the upper drum 2. A stator transformer 10 rigidly affixed to a predetermined portion of the upper surface of the lower drum 5 is kept at a predetermined gap with the rotor transformer 9. Here, reference numeral 14 denotes screws for affixing an outer housing(not shown) to the body of the rotor 11.
The operational description of the conventional head drum apparatus will now be explained.
When power is applied to the motor assembly 6 of the head drum apparatus, the rotor 11 is activated to generate the rotating force with an electric and magnetic operation at the motor assembly 6. Thereafter, the rotating force generated at the motor assembly 6 is applied to the rotating shaft 1 and rotates the upper drum 2 which is rigidly affixed to the rotating shaft 1. At this time, a tape wrapped around the upper drum 2 and the lower drum 5 is scanned as the upper drum 2 rotates. The audio and video signals read by the head assembly is applied to the rotor transformer 9 via a PCB(Printed Circuit Board) of the head assembly(not shown). The signals applied to the rotor transformer 9 is applied to the stator transformer 10 in a manner of non-contact and then is applied to the circuit section(not shown) thereof.
The detailed description of the structure of the upper drum 2 will now be explained.
As shown in FIG. 2, a stopper surface 21 and a chucking surface 22 are formed at the upper surface of the upper drum 2. A head-affixing surface 23 where the upper surface of the head assembly 7 is rigidly affixed thereto and a rotor transformer-affixing surface 24 where the upper surface of the rotor transformer 9 is rigidly affixed thereto are at the same height. At the inside portion thereof, the bearing-engaging surface 26 is formed.
In addition, as shown in FIG. 3, bearing-engaging surface 26 maintaining a predetermined gap with an upper surface of the upper bearing 3 is formed in order for having a step by the incline 28. Here, reference numeral 27 denotes an engaging surface where an outer surface of the rotating shaft 1 and the upper drum 2 is rigidly engaged.
However, the conventional head drum apparatus described above includes some problems in that the desired manufacturing accuracy cannot be obtained so that the height of the head-affixing surface 23 and the rotor transformer surface 24 is different from that of the bearing-engaging surface 26. Accordingly, an air-gap, which is one of the major points of making sure the performance of the head drum apparatus, between the rotor transformer 9 and the stator transformer 10 is difficult to be secured.
In addition, at the time of engaging the rotating shaft 1 into the upper drum 2, it is difficult to adjust the center between the engaging surface 27 of the upper drum 2 and the rotating shaft 1 as well as to engage the upper drum 2 vertically into the rotating shaft 1.